The origin of this persuasion is the dualism which gradualiy developed in European thought in respect to mind and Nature. At the beginning of the modern period Descartes expresses this dualism with the utmost distinctness. For him, there are material substances with spatial relations, and mental substances. The mental substances are external to the material substances. Neither type requires the other type for the completion of its essence. Their unexplained interrelations are unnecessary for their respective existences. In truth, this formulation of the problem in terms of minds and matter is unfortunate. It omits the lower forms of life, such as vegetation and the lower animal types. These forms touch upon human mentality at their highest, and upon inorganic Nature at their lowest.
The effect of this share division between Nature and life has poisoned all subsequent philosophy. Even when the co-ordinate
